Touch screens are widely applied today. The best known example of such a data processing system is the personal digital assistant (PDA) which is a compact personal computer providing a graphical screen for displaying objects of a graphical user interface, such as text strings and hyperlinks, graphical buttons, etc. In general, PDA's are not standard provided with a keyboard and/or mouse, but instead have a touch-sensitive display screen enabling a user to interact with the system. By touching the screen with a finger or stylus, the user can position a cursor within an application screen, press graphical buttons or draw characters on the screen. Increasingly, also other types of—mostly portable—devices are equipped with a touch screen, such as mobile phones or programmable remote controls.
Some tasks, such as entering text or making selections from lists are notoriously difficult on these kinds of devices. Most PDA's offer handwriting recognition, but this is still an unreliable technology. A widely applied solution is a virtual keyboard, which is a graphical representation of a computer keyboard displayed on the touch screen of the device, wherein each key is represented by a tiny button. The user can successively touch these buttons in order to enter the corresponding characters. Generally, such buttons are too small to be operated with a finger, which necessitates the use of a stylus. This problem can be solved to some extent by applying a zooming mechanism which, in response to touching the touch screen magnifies the objects displayed in the area around the touch position. An example of such a system with ‘auto zoom’ function is disclosed in U.S. Pat. No. 6,211,856. Such a system enables a user to operate small buttons or other objects, e.g. hyperlinks, without the need for a stylus and with increased accuracy.